Reverse bar coater



April 17, 1962 l.. HoRNBosTl-:L 3,029,779

REVERSE BAR coATER Filed oct. 15, 1958 Sttes atent lice 3,029,779REVERSE BAR COATER Lloyd Hornbostel, Beloit, Wis., assigner to BeloitIron Works, Beloit, Wis., a corporation of Wisconsin Filed Oct. 15,19555, Ser. No. 767,366 Claims. (Cl. 118-104) This invention relates toapparatus for coating a exible sheet or the like, and more particularly,to apparatus for applying a uniform coating to a travelling sheet suchas a paper web by lirst applying a coating material to the travellingweb which is then passed through a nip formed by a relatively largeradiused doctor roll and a relatively small radius bar or roll aboutwhich the travelling sheet may be wrapped.

Ordinarily, in the coating of a travelling sheet or web of fabric,plastic film, paper or the like, the sheet is backed by a supportingsurface and the coating is applied to the exposed side thereof using adoctor to smooth the coating material on the sheet and insure uniformapplication thereof. Although the instant invention may have use in thecoating of any of such sheets, it is particularly useful in the coatingof paper webs and will be described primarily with respect to this use.

It has been common in apparatus of the type described herein to trainthe travelling paper web over a relatively large radius backing roll andto use a smoothing blade or other small diameter rod or wire as adoctoring means. Such a procedure has a number of advantages, but alsohas certain disadvantages. For example, the small radiused smoothingmeans is not readily cleaned, is subject to damage and rapid wear, andmore importantly, tends to result in marking of the coating due to whatis termed split This behavior is common to all types of coatingapparatus, at least to a degree. It is a result of the fact that thecoating material wets both the surface of the web and the surface of thesmoothing means and as the surfaces separate, the uid itself must bepulled apart. This separation never occurs uniformly. This causesundesirable marks called tracks in the finished product.

lt is an object of the present invention to provide a mechanicalapparatus adapted to permit the smoothing of a coating material withoutthe loss of a part of the coating material onto the smoothing meansthereby avoiding the split described.

It is a further object of this invention to provide a coating apparatuswherein a flexible web travels over a small radiused supporting membersuch as a bar or roll which urges the web against a relatively largeradiused doctor roll, the surface of which at the nip is travelling in adirection opposite to the direction of travel of the web and which isprovided with a cleaning means after leaving the nip so that the doctorroll continually presents a clean surface to the coating as it leavesthe nip.

lt is a further object of this invention to provide a mechanicalapparatus for smoothing a coating material on a travelling web which iswrapped around a relatively small radiused supporting member which urgesthe web into contact with a smoothing means.

Other objects, features and advantages of the present invention will bemore fully apparent from the following detailed description taken inconnection with the accompanying drawings in which like referencecharacters are used to refer to like parts throughout and wherein:

FIGURE 1 is a diagrammatic elevational View of a coating apparatusembodying the instant invention.

FIGURE 2 is a fragmentary detail view showing a second embodiment of thenip forming supporting member shown in FIGURE 1.

FIGURE 3 is a fragmentary detailed view similar to FIGURE 2 but showinga third embodiment.

FIGURE 4 is a fragmentary detailed view similar to FIGURE 2 but showinga fourth embodiment.

Turning now to the drawing and in particular to FIG- URE l thereof,there is shown a typical coater applying coating to the side itla of atravelling web of paper 10. The coating may, for example, be initiallyapplied by passing the web 10 through the nip of a pair of rollers l1and 12, the lower roller 11 being partially immersed in a vat 13 ofcoating material 14. The side 10b of the web is then caused to Wrap, bya small angle, the reverse bar roller 15 which serves as a supportingmember to urge the coated side of the web into pressure contact with adoctor roller 16. The web passes over a roller 12a after leaving theroller 15 and the rollers 12 and 12a provide a carrying means for thesheet and are positioned to cause it to wrapv around a portion of thesurface of the roller 15. Similar carrying means are provided for thewebs 10a shown in FIGURES 2, 3 and 4 and are not shown to simplify thedrawings. A-fter leaving the nip formed between supporting member 15 anddoctor roller 16, the web carrying the smoothed coating may be fed toany suitable conventional drying apparatus,

The supporting member 15 as shown in FIGURE l, may be a solidcylindrical bar, the ends of which are journaled in supporting arms 17,which in turn are attached to any xed or'adjustably xed frame member 18.If desired, any conventional type of connection as by a flexible shaft,D, may be made from a motor M to the supporting member 15 in order tofacilitate cleaning the supporting member or to adjust its position inorder to distribute the wear thereon.

The supporting member or reverse bar 15 has a small radius so that theweb 1li travels through a change in direction, almost a sharp corner.The size of the radius is not critical but ispreferably within the rangefrom 1/30 to 1A@ of the diameter of the doctor roll. Due to thisrelationship, the nip pressure between the bar and the roll may be quitehigh without requiring the use of heavy structure and large total loads.The angle of lap of the web about the reversing bar can be varied tosuit the nature of the coating and the web being coated from nearly 0 toa turn of approximately 120. The doctor roll presents a clean surfacecontinually to the coating on the side 10a of the web 10 as it leavesthe nip by virtue of the fact that the doctor roller 16 is mounted `forrotation in such a direction that its surface at the nip is travellingin a direction opposite to the direction of travel of the web and byvirtue of the further fact that cleaning means 19 are provided for thesurface of the doctor roll after it leaves the nip and before returningthereto. 'Ihe cleaning means 19 may, for example, comprise a scraperblade or second doctor Z0 operating on the doctor roll 16 and a showerspray 21 in catch pan 22 which may be used to wash or otherwisecondition the surface of the doctor roll 16. With certain coatings beingapplied to the web 10, it is desirable to treat the surface of thedoctor roll with a release agent suited to the coating being used. Withany coating, it is desirable to clean the surface as by spraying waterfrom the shower means 21. It will, however, be understood that anydesired cleaning means may be used. v

In operation, the doctor roll 16 preferably rotates slowly in adirection such that the direction of travel of the surface of the rollat the smoothing nip is opposite to the direction of travel of the paperweb. It is preferred that the speed of linear travel of the surface ofthe doctor roll be from 10% to 85% of the paper speed but inthe oppositesurface direction. It vn'll, however, be understood that the mostdesirable speed for any particular application depends upon the type ofcoating being used. For any type of coating and for any speed, however,it is apparent that the relative sizes of the radii of the supportingmember and the doctor roll 16, coacting with the opposite direction ofsurface travel of the web 1t) and doctor roll 16, and with the cleaningmeans 19, insures that the portion 16a of the surface of the doctor roll16 entering the nip continually presents a clean surface to the coatingas it leaves the nip and thereby greatly reduces the tendency of thefluid coating on the web to adhere to this surface. Since the angle ofseparation between the web as it leaves the nip and the incoming portion16a of the doctor roll is relatively large, and since this portion 16ais an entirely clean surface, the above-discussed tendency of thecoating material to adhere to the smoothing surface and thereby resultin marking of the coating due to split is greatly reduced.

In FIGURE 2, there is shown an embodiment of the invention in which therotatable rod or wire 15 shown in FIGURE l is resiliently mounted in aslot 23 at the end of an arm 24. At the rear of the slot 23 is a tube 25of iiexible material such as rubber which is adapted to expand orcontract in accordance with the pressure variations of air passedthrough the tube. Tube 25 is positioned at the back of slot 23 and ablock 26 of any suitable self-lubricating material such as graphite or asynthetic resinous plastic is interposed between the tube 25 and the rod15. Block 26 is so shaped as to mate with the normal curvature of thesurfaces of tube 25 and rod 15. The arm 2li, tube 23 and rod 15 as wellas the block 26, are shown in an elevational sectional view. It will, ofcourse, be understood that the ends of the rod 15 are mounted inresilient or movable journal means in order to accommodate the slightmotion to and away from the doctor roller 16 of the rod 15 in responseto change of air pressure in the tube 23. As in the embodiment of FIGUREl, the rod 15 can be rotated in order to distribute wear and to preventthe accumulation of fiber and other particles.

In FIGURE 3, there is illustrated another modification wherein the smallradius rod consists of a rigid tube 15a having a hollow interior andhaving its outer wall provided with a series of small holes 27 drilledtherein to provide an outlet for air under pressure which is suppliedthrough the interior of the tube. A closely spaced series of these smalldrilled holes 27 permits air to be introduced under the side 1Gb of theweb as a means of lubrication to reduce the friction of the travellingweb over the bar 15a. In the embodiment of FIGURE 3, it will be notedthat the bar 15a is rigidly mounted on the end of an adjustable arm 2S.

In FIGURE 4, there is illustrated an embodiment of the invention inwhich the small radiused rod 15 or 15a is replaced by a bar 29 having atapered and rounded end portion 3G which affords a surface at the end ofthc rod contacted by the web 10 which has again a radius small bycomparison to the diameter of the doctor roller 16. Except for thedilference in the detailed nature of the supporting member affording thesmall radiused surface, the embodiments shown in FIGURES 2, 3 and 4 arethe same as that shown completely in FIGURE 1. As will be noted from thevarious figures of the drawing, the small radiused supporting member maybe either a rigidly fixed bar such as shown in FIGURE 4, a tube havingair outlets for web lubrication purposes such as shown in FIGURE 3, aresiliently and rotatably mounted rod such as shown in FIGURE 2, orsimply a rotatably mounted rod such as shown in FIGURE l. In any ofthese embodiments, the advantages discussed above in connection withFIGURE 1 may readily be obtained.

While particular preferred exemplary embodiments of the invention havenow been described, it will be understood that modications andvariations may be eected therein without departing from the spirit andscope of the novel concepts of the present invention as defined by thefollowing claims.

I claim as my invention:

1. Apparatus for coating a travelling sheet comprising, a doctor rollhaving a first radius of curvature, a sheet supporting member which hasat least one Surface with a second radius of curvature small bycomparison to that of said doctor roll and which is wrapped by saidsheet, said surface of said supporting member defining with said doctorroll a nip through which the sheet passes, means for carrying atraveling sheet wrapped over said surface of the sheet supportingmember, coating means at the oncoming side of the nip and on the doctorroll side of the sheet to apply coating to the sheet, said supportingmember urging said sheet into pressure contact with said doctor roll tosmooth and level said coating, the surface of said doctor roll at saidnip moving in a direction of travel opposite to the direction of travelof said sheet, and means to clean excess coating from the surface ofsaid doctor roll after said surface leaves said nip.

2. Apparatus for coating a travelling sheet comprising, a doctor rollhaving a first radius of curvature, a sheet supporting member comprisinga rotatable rod with a surface which has a second radius of curvaturesmall by comparison to that of said doctor roll and which is wrapped bysaid sheet, said rod defining with said doctor roll a nip through whichthe sheet passes, means for carrying a traveling sheet wrapped over saidsurface, coating means at the oncoming side of the nip and on the doctorroll side of the sheet to apply coating to the sheet, said rod urgingsaid sheet into pressure contact with said doctor roll to smooth andlevel said coating, the surface of said doctor roll at said nip movingin a direction of travel opposite to the direction of travel of saidsheet, and cleaning means comprising a liquid spray and scraping meansto clean excess coating from the surface of said doctor roll after saidsurface leaves said nip.

3. Apparatus for coating a travelling sheet comprising, a doctor rollhaving a first radius of curvature, a sheet supporting member comprisinga resiliently mounted rod having a surface which has a second radius ofcurvature small by comparison to that of said doctor roll and which iswrapped by said sheet, said rod being mounted to dene with said doctorroll a nip through which the sheet passes, means for carrying a sheetwrapped over said surface, coating means at the oncoming side of the nipand on the doctor roll side of the sheet to apply coating to the sheet,said rod urging said sheet into pressure Contact with said doctor rollto smooth and level said coating, the surface of said doctor roll atsaid nip moving in a direction of travel opposite to the direction oftravel of said sheet, and means to clean excess coating from the surfaceof said doctor roll after said surface leaves said nip.

4. Apparatus for coating a travelling sheet comprising, a doctor rollhaving a first radius of curvature, a sheet supporting member comprisinga rigidly mounted tube with a surface which has a radius of curvaturesmall by comparison to that of said doctor roll and which is wrapped bysaid sheet, said tube defining with said doctor roll a nip through whichthe sheet passes, said tube being provided with a plurality ofpressurized air outlet holes to lubricate said travelling sheet, meansfor carrying a sheet wrapped over said surface, coating means at theoncoming side of the nip and on the doctor roll side of the sheet toapply coating to the sheet, said supporting tube urging said sheet intopressure contact with said doctor roll to smooth and level said coating,the surface of said doctor roll at said nip moving in a direction oftravel opposite to the direction of travel of said sheet, and means toclean excess coating from the surface of said doctor roll after saidsurface leaves said nip.

5. Apparatus for coating a travelling sheet comprising, a doctor rollhaving a first radius of curvature, a sheet supporting member comprisinga rigid bar having a tapered end which has a radius of curvature smallby comparison to that of said doctor roll and which is Wrapped by saidsheet, said tapered end of said bar dening with said doctor roll a nipthrough which the sheet passes, means for carrying a sheet Wrapped oversaid end, coating means at the oncoming side of the nip and on thedoctor roll side of the sheet to apply coating to the sheet, saidsupporting bar urging said sheet into pressure Contact with said doctorroll to smooth and leve1 said coating, the surface of said doctor rollat said nip moving in a direction of travel opposite to the direction oftravel of said sheet, and means to clean excess coating from the Surfaceof said doctor roll after said surface leaves said nip.

UNTED STATES PATENTS Goldsmith Oct. 4, 1904 Francis Mar. 16, 1920Bradner Mar; 14, 1933 Coates May 1, 1934 Johnson Aug. 12, 1941 Mulloy etal. July 3, 1951 Brink June 16, 1953 Pompei' July 8, 1958 HornbostelNov. 25, 1958 Wommack et al. Dec. 22, 1959

